RFR: 8172905: Minor startup cleanup of CallSite and MethodType

[Claes Redestad]

Hi,

as a follow-up to JDK-8086045, further analysis has found a number of 
small, simple improvements that can be made to further improve startup 
characteristics of typical usage of java.lang.invoke:

- CallSite::<clinit> looks up two MethodHandles that aren't used in many 
typical applications and should be lazily constructed
- CallSite.CONTEXT_OFFSET is calculated but never used
- The ConcurrentHashMap in MethodType$ConcurrentWeakInternSet is resized 
multiple times even for relatively trivial tests, and initializing it to 
a larger size is footprint neutral but beneficial to startup to many 
applications

Bug: https://bugs.openjdk.java.net/browse/JDK-8172905
Webrev: http://cr.openjdk.java.net/~redestad/8172905/webrev.01/

This small set of relatively non-intrusive changes has a measurable 
impact to startup - generates fewer classes on some tests, does less 
work on all - which partially help with a number of startup regressions 
tracked in 9 due to heavier and earlier use of j.l.invoke.

Thanks!

/Claes